Due to the rapid increase in quantity of municipal waste, several approaches for disposing of municipal waste have been proposed and, in fact, some of them have been put into practice. Among those, thermal disposal such as incineration and/or pyrolysis has proved to be satisfactory to some extent. The pyrolyzing process is particularly, useful in the point that it provides pyrolysis gas as fuel from the waste to be discarded. However, municipal waste contains many constituents and they may generate harmful gas such as HCl, H.sub.2 S, SOx, etc. when they contain vinyl chloride, etc. and are pyrolyzed in a thermal reactor such as a fluidized bed. Such harmful gas erodes the apparatus and/or creates the problem of environmental pollution.
In order to minimize such drawbacks or to eliminate the harmful gas, materials reacting with the harmful gas to produce harmless compounds have heretofore been supplied to a pyrolyzing reactor. Suitable materials for such purpose are compounds of alkali earth metals such as dolomite, quick lime and slaked lime, etc.
There are several ways for supplying such compounds of alkali earth metals (hereinafter simply referred to as "absorbing agent"). For instance, the absorbing agent comprising particles ranging in size from approximately 1 m/m to 5 m/m is charged to a fluidizing bed; powdery absorbing agent having particle size below 0.5 m/m is charged either to a free boad portion in a fluidized reactor or to the fluidized bed. In any of the processes for supplying the absorbing agent, it is necessary, in order to effectively eliminate harmful gas, to supply the absorbing agent in a quantity 4 or 5 times, in equivalent, the quantity of "Cl" contained in the material or waste to be pyrolyzed. Accordingly, in the prior art for charging the agent, only approximately 20% of the charged absorbing agent is effectively utilized and the rest thereof, i.e. approximately 80% of the charged agent is discharged out of the system without being reacted and utilized thereby wasting a considerable proportion of the absorbing agent.
Therefore, the general practice has been to charge the recovered absorbing agent together with dust and char collected at a dry type collector such as cyclone. However, the dry type collector can not collect all the particles of the absorbing agent, etc. because some are of a size below the collecting capacity of the dry type collector. Therefore, particles of the absorbing agent not trapped by the dry type collector are subjected to a wet type cleaning process so that they are separated together with liquid or water from the generated pyrolysis gas. However, the pyrolysis gas generated carries other foreign matter or impurities such as oil, tar or the like which remain therein as unvaporized or ungasified residue and these items are also picked up by the cleaning water from the pyrolysis gas. In the wet type collector, the solid particles of the char and absorbing agent and a part of the oil and tar aggregate and settle in the water from which they are easily separated from the water to be discharged. However, the rest of the oil and tar in the cleaning water remain floating on the surface of the water or suspended in the water, because the amount of the tar and oil is relatively rich compared to that of the solid items introduced and involved in the cleaning water. Thus, it has been quite difficult to separate those floating and suspended oil and tar components from the water, so the discharged water is likely to be contaminated with these particles.